Microsoft co-founder Bill Gates is ready for his next endeavor: joining the fight against Alzheimer's disease.

Gates revealed Monday that he invested $50 million in the Dementia Discovery Fund, which is working on new approaches to treating dementia. Gates also plans to invest an additional $50 million in start-ups working on Alzheimer's research, according to an interview with Reuters.

"It’s a miracle that people are living so much longer, but longer life expectancies alone are not enough," wrote Gates in a blog post. "People should be able to enjoy their later years—and we need a breakthrough in Alzheimer’s to fulfill that."

Gates said this is a personal investment, not one offered through the Bill & Melinda Gates Foundation, which has invested in research to stop the spread of diseases such as HIV.

Gates said he spent the last year learning about the disease, speaking with researchers and other experts about what they need to fight Alzheimer's. Gates said progress is needed in five areas, including better use of data and a better understanding about how the disease unfolds.

Gates is familiar with the impact Alzheimer's has on families, both financially and emotionally. Gates cites a family history with the disease.

"I know how awful it is to watch people you love struggle as the disease robs them of their mental capacity, and there is nothing you can do about it," Gates wrote. "It feels a lot like you’re experiencing a gradual death of the person that you knew."

According to the Alzheimer's Association, the disease is the sixth leading cause of death in the U.S. More than 5 million Americans live with Alzheimer's. By 2050, the number could rise to 16 million.